Mod Store worth it for new player?

If you just unlocked mods, don't buy any from the mod store. It'll only hinder your progress. Use all mod energy on mod challenges, never on slicing mats, and you'll find roughly one decent mod a day, and great one a week, and one God mod a month on average. Mod store shows some tempting ones, but they very rarely live up to expectations, and you need the currency elsewhere. Trust me, I've made that mistake before.